Seth,
Dullcote will:
1) In general, darken the effect of the chalk application. You will come to appreciate just how much darkening only through experience and allow for this effect when first applying the chalk.
2) If you use the matte/dull version of Dullcote lightly it should have little effect on the desired dullness. So as to not dislodge the chalk powder when I spray with Dullcote, I hold the spray can at least 1 foot/ 30 cms away and wave the can about as I'm spraying. Again, practice, practice, practice.
This whole weathering process can be explained in words just so far. You just gotta get your hands dirty/sticky and learn by doing. Don't be afraid to make mistakes. Sometimes the screw-ups can look terrific. First mistake = trying to do too much in one pass - sneak up on your desired outcome. That's why I love working with pastel chalks. If I don't like to effect, I can just blow the chalk away = mostly - the little chalk left behind can oft leave a wonderful subtle base on which to proceed.
Dan
